One example of such oil immersed solenoid is shown in FIG. 4(a). The oil immersed solenoid is used to control the oil pressure and flow rate of operating oil flowing in a valve device (not shown) that is, for example, an oil-pressure device. To be specific, in an oil immersed solenoid 1, when a command electric signal (exciting current) is transmitted to an exciting coil 2, pulling force (pulling force in a left direction in FIG. 4(a)) corresponding to the magnitude of the command electric signal is generated at a fixed magnetic pole portion 3, and the fixed magnetic pole portion 3 can pull a movable core 4 by the pulling force. When the movable core 4 is pulled, a rod 5 provided at the movable core 4 presses, for example, a spool (not shown) of a valve device (not shown) in the left direction in FIG. 4(a). This pressing force balances push-back force (push-back force in a right direction in FIG. 4(a)) based on, for example, spring force or pilot pressure applied to the spool. The spool stops at a position where the pressing force and the push-back force are balanced. With this, the oil pressure and flow rate of the operating oil flowing in the valve device can be controlled so as to be proportional to the command electric signal.
Then, as shown in FIG. 4(a), an annular gap 63 is formed between a tip end portion of a cylindrical second guide 20 and a rear end portion of the fixed magnetic pole portion 3. The reason why the gap 63 is formed is because a part of magnetic flux lines passing through the fixed magnetic pole portion 3 are prevented from leaking to the second guide 20 without passing through the movable core 4. Almost all of the magnetic flux lines generated in the fixed magnetic pole portion 3 are caused to pass through the movable core 4, and in this way the fixed magnetic pole portion 3 can efficiently pull the movable core 4.
Moreover, in order to cause the movable core 4 to smoothly move forward and backward and prevent corrosion, a space 6 in which the movable core 4 is accommodated is filled with oil, such as the operating oil. Further, in order that the oil in the space 6 can freely move between a space formed on a front side of the movable core 4 and a space formed on a rear side of the movable core 4 when the movable core 4 shown in FIG. 4(a) moves in a front-rear direction, two communication grooves 62 are formed on a side surface of the movable core 4 so as to extend in a center axis direction.
Another example of the oil immersed solenoid is disclosed in Japanese Laid-Open Utility Model Application Publication No. 6-2620 (see PTL 1, for example).